The present invention generally relates to a recording method and a recording apparatus. More specifically, the present invention is directed to a printing method and a printer for jetting a recording fluid such as ink in a form of fluid droplets and for adhering the recording fluid on a recording member in a dot shape to execute a recording operation.
Very recently, strong needs are rapidly made of producing hard copies in color in connection with marketing of color video cameras and color computer graphics. To meet these requirements, various color hard copying recording systems have been proposed, for instance, sublimination type heat transfer systems, thermal melting transfer systems, ink jet systems, electrophotographing systems, thermal developing silver halide systems and so on. Among these recording systems, the method capable of simply outputting high quality images by way of a simple apparatus may be mainly classified into the dye diffusion thermal transfer method and the ink jet method.
In the dye diffusion thermal transfer method among these recording systems, either the ink ribbon or the sheet on which the ink layer is coated, and the transferred member are closely attached to each other under constant pressure, to which heat corresponding to the image information is applied from the heat sensitive recording head located on the ink sheet. Then, the transfer dye is thermally transferred in response to the head amount applied from the ink sheet to the receiving layer. In the ink layer, the transfer dye with high density is distributed in the proper binder resin. As the transferred member, there is a printing paper on which the dy accepting resin for accepting the transferred dy is coated.
In a so-called "thermal transfer" method where the above-described operations are repeatedly performed as to the three primary colors of the subtraction mixture color, namely the image signals solved into yellow, magenta, and cyan, the full color image having the continuous gradation can be produced. This thermal transfer system is known as the excellent recording technique capable of producing the high grade images equivalent to the silver halide color photographic images in a compact and maintenance free characteristic.
FIG. 1 is a front view for schematically showing a major portion of this thermal transfer type printer.
In FIG. 1, a heat sensitive recording head (will be referred to as a "thermal head" hereinafter) 100 is located opposite to a platen roller 101. An ink sheet 102 made of an ink layer 102a on a base film 102b, and a recording paper (recorded member) 103 provided with a type accepting resin layer 103a on a paper 103b are sandwiched between the thermal head 100 and the platen roller 101. These members are traveled while being depressed against the thermal head 100 by the rotating platen roller 101.
Then, the ink (transfer dye) contained in the ink layer 102a selectively heated by the thermal head 100 is transferred in a dot form to the dye accepting resin layer 103a of the recording paper 103 to thereby execute the thermal transfer recording operation. As such a thermal transfer recording operation, the serial system and the line system are employed. That is, in the serial system, the thermal head is scanned along the direction perpendicular to the travel direction of the recording paper 103. In the line system, one thermal head is fixedly arranged along the direction perpendicular to the travel direction of the recording paper. This non-impact recording method is widely spread in view of such a fact that the recording noise is extremely low during the recording operation.
Different from this thermal transfer system, a so-termed "ink jet recording method" is known in the field. This ink jet recording system is capable of performing the highspeed recording operation. Moreover, the recording operation can be done by employing a so-called "normal paper" without requiring a specific fixing process. Therefore, this ink jet recording system will gradually constitute the major recording system capable of reproducing the images such as computer graphics as hard copies.
As described in Japanese Patent Publication No. 61-59911 published in 1986 and Japanese Patent Publication No. 5-217 published in 1993, the above-explained ink jet type printer is such that in response to image information, recording fluid droplets are jetted from nozzles provided in a recording heads by way of the electrostatic absorbing method, the electro-mechanical converting method (piezoelectric element method), and the thermal method (bubble jet method), and then these recording fluid droplets are adhered onto recording materials for recording operation.
As a result, since substantial no waste material is produced and running cost is low, this ink jet type printer becomes popular.
On the other hand, in a so-called "on-demand type ink jet type printer apparatus" (will be simply referred to as an "ink jet printer" hereinafter), ink droplets are jetted from nozzles in response to recording signals so as to record the content of this recording signal on a recording member such as a paper and a film. Since this ink jet printer can be made compact and low cost, the ink jet printers are rapidly spread in recent years.
In general, for example, piezoelectric elements and heating elements are employed so as to jet ink droplets in such an ink jet printer. In a piezoelectric element type ink jet printer, the piezoelectric element is deformed to thereby give pressure to the ink, and thus the ink droplets are jetted from the nozzles.
FIG. 2A to FIG. 2C illustrate one conventional ink jet printer (e.g., on-demand type ink jet printer).
First, a structure of a printing head shown in FIG. 2A is constructed of a cylindrical casing 111 made of glass, and a cylindrical electrostrictive vibrating element (piezoelectric element) 112 provided on an outer side surface of this casing 111. On both edge portions of this casing 111, there are provided an ink supply port 114 for filling ink 110 into an ink chamber 113 of the casing 111, and a nozzle 116 and also an orifice portion 117, which may jet the ink as ink fluid droplets 115.
Then, when a predetermined voltage is applied from a voltage generator 118 to the electrostrictive vibrating element 112, this electrostrictive vibrating element 112 is deformed which may cause the capacity of the ink chamber 113 within the casing 111 to be changed. In response to this capacity change, the inner pressure of the ink chamber 113 is increased, so that the ink droplets 115 are jetted from the nozzle 116.
As a consequence, when the voltage generator 118 is driven in response to arbitrary print information, the ink droplets 115 can be jetted from the nozzle 116 based on this print information. Then, the jetted ink droplets 115 are adhered onto a recording paper (not shown in detail) functioning as a recording medium to execute the printing operation.
Also, FIG. 2B represents an example of a printing head with employment of a plane-shaped electrostrictive vibrating element. In this printing head, one surface of a casing 121 made of a proper material is constituted as a vibrating plate 122, and an electrostrictive vibrating element 123 is adhered on the outer surface of this vibrating plate 122, so that a so-called "bimorph plate" is fabricated. Furthermore, on both edge portions of this casing 121 there are provided an ink supply port 125 for filling ink 120 into an ink chamber 124 of the casing 121, and a nozzle 127 and also an orifice portion 128, which may jet the ink as ink fluid droplets 126.
Then, when a predetermined voltage is applied from a voltage generator 129 to the electrostrictive vibrating element 123, this electrostrictive vibrating element 123 is deformed which may cause the capacity of the ink chamber 124 within the casing 121 to be changed. In response to this capacity change, the inner pressure of the ink chamber 124 is increased, so that the ink droplets 126 are jetted from the nozzle 127.
As a consequence, when the voltage generator 129 is driven in response to arbitrary print information, the ink droplets 126 can be jetted from the nozzle 127 based on this print information. Then, the jetted ink droplets 126 are adhered onto a recording paper (not shown in detail) functioning as a recording medium to execute the printing operation.
Further, FIG. 2C indicates an example of a so-termed "Stemme (two-chamber) type printing head". In this printing head, one surface of a casing 131 made of an arbitrary material is made as a vibrating plate 132, and an electrostrictive vibrating element 133 is adhered onto an outer surface of this vibrating plate 132, which may constitute a so-called "bimorph plate". A pressure chamber 134 is formed in the casing 131, and an ink supply path 135 is provided, while being communicated with this pressure chamber 134.
Also, an ink supply port 136 is formed which may fill ink 130 into the ink supply path 135. A nozzle 138 and an orifice portion 139, which may jet the ink as ink fluid droplets 137, are provided at a position opposite to a communication portion between this ink supply path 135 and the pressure chamber 134.
Then, when a predetermined voltage is applied from a voltage generator 140 to the electrostrictive vibrating element 133, this electrostrictive vibrating element 133 is deformed which may cause the capacity of the ink chamber 134 within the casing 13 to be changed. In response to this capacity change, the inner pressure of the ink chamber 134 is increased, so that the ink droplets 137 are jetted from the nozzle 138.
As a consequence, when the voltage generator 140 is driven in response to arbitrary print information, the ink droplets 137 can be jetted from the nozzle 138 based on this print information. Then, the jetted ink droplets 137 are adhered onto a recording paper (not shown in detail) functioning as a recording medium to execute the printing operation.
On the other hand, FIGS. 3A, 3B, 3C and 3D represent other examples of printing heads used in the above-described ink jet printer (for instance, on-demand type ink jet printer), in which ink is jetted by using, for example, a heating element.
In accordance with the structure of this printing head, a heating element 152 is provided inside a nozzle 151, and power is supplied to this heating element 152 so as to instantaneously vaporize ink 150 inside the nozzle 151. Then, in response to pressure of bubbles produced by this ink vaporization, ink droplets 157 are jetted from a tip portion 154.
That is, in FIG. 3A, when power is supplied to the heating element 152, the ink 150 in contact with the heating element 152 is heated to be vaporized, so that a plurality of small bubbles 156 are produced. These plural bubbles 156 are combined with each other to become a single large bubble 157 (see FIG. 3B). Thus, the ink 150 present in the nozzle 151 is extruded from the tip portion 154 in response to pressure of this large bubble 157, as shown in FIG. 3C.
Then, when the supply of power to the heating element 152 is interrupted under such a condition as shown in FIG. 3C, the bubble 157 is rapidly reduced, so that the pressure in the nozzle 151 is lowered. As a result, the ink extruded from the tip portion 154 is separated from the ink 150 stored in the nozzle 151, and as shown in FIG. 3D, the separated ink is jetted as ink droplets 157.
As a consequence, when the heating element 152 is driven based on arbitrary print information, the ink droplets 157 can be jetted from the nozzle 151 in response to this print information. Then, the ink droplets 157 are adhered on a recording paper (not shown) functioning as a recording medium.
On the other hand, when each of the respective printing heads is used to record a desirable image on a recording paper, as schematically shown in FIG. 4, for example, while the serial type printing head 16 is scanned along the main scanning direction with respect to the recording paper 180, the ink is jetted in response to the image information so as to be adhered as the pixel 181 in the dot shape. It should be understood that this recording operation is carried out based on two values, i.e., jetting of the ink droplets, and non-jetting of the ink droplets.
In this case, when the image quality of the recorded dot (pixel) is improved by the gradation representation (half tone), there is such a case that the print information is formed in, for instance, 8 bits (=256 gradation). To the contrary, when the gradation (6 bits=64 gradation) of the intermediate gradation (half tone) printed by the printer apparatus is smaller than 256 gradation, the gradation extending method such as a so-called "multi-gradation dither method" (as one example, multi-gradation error diffusion method) is employed.
That is to say, for example, in the multi-gradation error diffusion method, as represented in FIG. 5, a level of an arbitrary pixel "A" for constituting an image is replaced from an originally printed level X (256 gradation) into an actually printed level X' (normally, 4, 6, 8, 16, 32, 64 gradation, in this case, 64 gradation). In this case, the following methods are employed. That is, the level X' to be replaced is set tot he level being nearest the level X. Alternatively absolute values of differences between plural levels realized by the level X' and the level X are replaced as probabilities. In the latter method, there are possibilities that the level X' is replaced by all of the realizable levels.
Moreover, an error portion ".epsilon." between the level X and the level X' is distributed to pixels around the pixel "A" so as to be added. As indicated in FIG. 5, as to this distribution method, there are the following methods. In one distribution method, (7/16).epsilon. is distributed to a pixel subsequent to the pixel A, (3/16).epsilon. is distributed to a pixel before the next scanning line, (5/16).epsilon. is distributed to a pixel just under the pixel A, and (1/16).epsilon. is distributed to a pixel after the next scanning line. In another distribution method, the error portion is distributed only to an arbitrary one pixel at probability of the respective distribution rates.
It should be noted that the error portion .epsilon. owns codes of ".+-.". The errors of the peripheral pixels to which the errors have been distributed are calculated as to the value, added with the distributed errors. Furthermore, when the value added with the distributed error exceeds a maximum printing level or a minimum printing level in a printable range, the value exceeding this maximum printing level or minimum level may be clipped. Otherwise, this exceeding portion is again distributed to the peripheral pixels in the above-described rate, or probability in a similar calculation manner to the above error portion ".epsilon.".
In this manner, the error portion .epsilon. of the pixel A is distributed to the peripheral pixels, so that the printing error is distributed. This is carried out over the overall input image to thereby form image data to be printed. As a result, the gradation of the image which is obtained by printing out the print information can be essentially enlarged (for example, 64 gradation is enlarged into 256 gradation). The above-described distribution rate and numeral values are merely one example, and therefore may be varied in accordance with the differences of the gradation to be converted, and ranges (number) of pixels to which the error portions are distributed.
As a consequence, for instance, since the above-described dither method is employed in the host computer, the print information of 64 gradation which can be printed by the printer apparatuses can be formed from the print information of 256 gradation (=8 bits) formed in the host computer. Then, in this case, for example, the print information of 64 gradation is expressed by, for instance, 6 bits.
In FIG. 6, there is shown such a condition that the input data (print information) shown by a broken line is converted along the X direction by way of the above-described multi-gradation error diffusion method, namely this input data having the corresponding gradation every dots along the main scanning direction of the print head.
In this case, in the image to be printed out, a total amount of the ink fluids jetted from the printing head at a certain portion is determined based on the characteristic of the ink fluids, the characteristic of the recording paper, and the printing speed. However, the ink droplets on the recording paper are spread to be mixed with each other, resulting in deteriorations of the color reproducing characteristic and of the image quality, and further of the resolution. These deteriorations are commenced at the minimum printing density.
Accordingly, in such a case that the image to be printed owns the continuous expansion higher than the minimum printing density, particularly, in the multi-gradation error diffusion method, while the ink jetted so as to form one pixel is not fixed on the recording paper, the succeeding ink is jetted to the adjoining position (otherwise, same position) immediately after the first-mentioned ink is jetted. Thus, the total ink amount is increased, so that the ink droplets are spread. Since drying of the ink droplets is delayed, the adjoining ink droplets are mixed with each other, resulting in deteriorations of the color representing characteristic, of the image quality, and of the resolution. To avoid this difficulty, expensive print-dedicated recording papers are used, and there is a limitation in the printing speed.
This problem is particularly produced when the print-dedicated recording paper is not used (namely, low-cost normal paper, and reproduced paper, i.e., general-purpose recording papers), when the environmental temperatures during the printing operation are lowered, or when the printing head is scanned in high speed. Even when the print-dedicated recording paper is employed, a similar problem may occur. Also, in a two-fluid mixing type printer, so-called "carrier jet type printer" (will be discussed later), when the extra-jetted ink is jetted on the recording paper, this extra-jetted ink may give the large adverse influences to the image quality. Therefore, there is another problem that the intermediate gradation (half tone) could not be achieved.
However, to improve image qualities of recorded dots (pixels) by way of gradation (half tone) representations in such an ink jet printer, the Applicant has proposed the novel carrier jet type printing system as disclosed in Japanese patent Application No. 7-254250 filed on Sep. 29, 1995. In this novel carrier jet type printing system, any one of the dilution fluid and the ink is quantified in accordance with the print information, and the other item is mixed in a preselected amount to produce the mixture fluid, and then this mixture fluid is used to print out a half tone. This novel two-fluid mixing type printing system will be later discussed more in detail.